It is known that ceramics consisting of some kinds of metallic oxides or their composite materials can emit far infrared rays having a wave-length not less than 3 microns, in particular, of 4-25 microns at the normal temperature.
Until now, far infrared rays emitted by ceramics have been utilized for heating, drying, or disinfecting foods in a short wave length range at high temperature. Recently, however, utilization of far infrared rays in a long wave length area at or below the room temperature has been noted; as a result, various products utilizing these ceramics have been proposed in order to maintain the freshness and sanitation of foods.
Since these ceramics can be easily formed at or near room temperature, powder ceramics are generally kneaded into polyolefin resins etc. to be formed into a film, a sheet, or other moldings.
However, compositions obtained by kneading powder ceramics into resins such as polyethylene or polypropylene are low in transmission factors of far infrared rays having a wave-length of 3-25 microns, in particular 4-14 microns, and therefore, far infrared rays emitted from ceramics were not able to be satisfactorily utilized.